Truth is a complete defense to a defamation charge, but a defendant does not have to prove the literal truth of a defamatory statement to prevail. An effective defense can rely on the substantial truth doctrine. Under the substantial truth doctrine, a defamatory statement is First Amendment-protected if it is factually similar to the pleaded truth, and does not differ from the truth by more than immaterial details. This article presents and analyzes the theory, application, and constitutional foundations of the substantial truth doctrine. It concludes that the doctrine promotes the values of the First Amendment by reducing the risk of self-censorship, yet preserves defamation law's reputational protection and compensatory function.